Method of manufacturing battery lid

ABSTRACT

A cathode lid of a battery container having a peripheral portion U letter shaped in section, with the outer peripheral side formed thicker than the inner peripheral side, and a side formed thicker than the inner peripheral side, and a method of manufacturing the same. In a process of manufacture of the anode lid, the periphery of a blank of a disk is bent in one direction vertical to the surface thereof, thereby to achieve a structure of a vessel having a bent periphery and then the vessel structure is subjected to paired working processes of punch and knockout, whereby a pressing force is exerted so that the edge of the bent periphery and the central portion of the main flat portion of the blank comes to to be close to each other in the direction vertical to the surface of the blank. As a result, the periphery is formed to be U letter shaped in section, while the central portion is maintained flat.

This is a division of application Ser. No. 251,539, filed Apr. 6, 1981,now U.S. Pat. No. 4,419,420.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lid of a battery container and amethod of manufacturing the same. More specifically, the presentinvention is directed to an improvement in geometry and structure of acurled portion of a lid and a main body of a battery container largelyinfluencing leakage of an electrolyte and also to an improvement in amethod for manufacturing such lid.

2. Description of the Prior Art

FIG. 1 is a front view, partially in section, showing a conventionalsilver oxide battery for explaining the prior art of interest to thepresent invention. FIGS. 2 to 8 are end views of mid-sectioned partshowing in succession different steps of a method of manufacturing thelid used in the FIG. 1 battery.

The silver oxide battery shown is a so-called button type battery whichhas been widely used as a power supply for an electronic wristwatch, forexample. The battery container comprises an cathode container element 1constituting a main body of the battery container and a anode containerelement constituting a lid of the battery container. The cathodecontainer element 1 or the main body is made of an iron plate nickelplated and an cathode material 2, a separator 3 and a anode material 4are in succession placed in a laminated fashion in the cathodecontainer 1. The anode container element 5 or the lid is then placed onthe anode material 4. The anode container element 5 is made of stainlesssteel and a copper layer is formed on the inner surface thereof, whilethe outer surface thereof is formed with a nickel layer.

The anode container element 5 is formed with a periphery portion 6 Uletter shaped in section. A packing 7 is disposed substantially outsideof the peripheral portion 6 and, when the opening edge of the anodecontainer element 1 is curled inside, the same is engaged with theperipheral portion 6 of the cathode container element 5 with the packing7 therebetween. As a result, a sealing structure for preventing aleakage phenomenon of an electrolyte is achieved.

Since the above described anode container element 5 has the peripheralportion 6 folded in a U letter shape in section, the periphery of theanode container element has an increased strength to buckling. However,since the hardness of a portion being curled largely contributes toprevention of leakage of an electrolyte, a much more increased hardnessis desired.

An insufficient hardness of the peripheral portion 6 of the conventionalanode container element 5 which is engaged with the opening edge of thecathode container element 1 is presumably caused by a conventionalmanufacturing process to be set forth in the following. According to aconventional manufacturing process, a blank 8 is cut to a desired shapeand size is prepared as shown in FIG. 2. Then the blank 8 is subjectedto a pressing process by means of an upper drawing die 9 and a lowerdrawing die 10, whereby the blank 8 undergoes a first drawing process.At that time, the outer peripheral portion of the blank 8 is stronglysandwitched to prevent from wrinkling, so that the thickness of theouter peripheral portion is decreased. Then the blank 8 is subjected toa second drawing process by means of an upper drawing die 11 and a lowerdrawing die 12, as shown in FIG. 4. Again in this step the thickness ofthe outer peripheral portion of a material being worked 13 is decreased.Then the material being worked 13 is subjected to cutting to be trimmedto a desired size in diameter, as shown in FIG. 5. Thereafter, as shownin FIG. 6, the flange portion 14 at the outer periphery of the materialbeing processed 13 is slightly bent preparatively upward as viewed.Then, as shown in FIG. 7, the flange portion 14 of the material beingworked 13 is fully bent so that the periphery of the material beingworked 13 may be U letter shaped in section. Then ultimately, as shownin FIG. 8, the flange portion 14 is further pressed, whereby the flangeportion 14 is brought to be closer to the main body portion of thematerial 13. Thus the anode container element 5 as shown in FIG. 8 isobtained and the flange portion 14 constitutes a portion of theabovedescribed peripheral portion 6 U letter shaped in section.

It has been observed that according to such conventional process thesteps as shown in FIGS. 3 and 4 and 6 to 8 involve some problems. Thiswill be described in more detail with reference to FIG. 9, which showsin an enlarged manner the peripheral portion of the lid.

A first problem is that the thickness of the outer peripheral portion ofthe blank 8 or the material being worked 13 is decreased to be made thinat the steps shown in FIGS. 3 and 4. The outer peripheral portionthereof is ultimately brought to the position of the outer peripheralside 6a of the peripheral portion 6 U letter shaped in section.Accordingly, the outer peripheral side 6a thus made thin naturallyexhibits an inferior strength. A second problem arises when the flangeportion 14 is folded so that the peripheral portion 6 U letter shaped insection is formed at the steps shown in FIGS. 6 to 8. More specifically,at the steps shown in FIGS. 6 and 7 only a natural bent portion isformed by folding the flange portion 14 and no work hardening is notperformed. The FIG. 8 step is then carried out in such situation and theouter peripheral side 6a of the peripheral portion 6 U letter shaped insection is brought to be close to the inner peripheral side 6b so thatthe spacing may be decreased, as shown in FIG. 9. As a result, the bentportion 6c becomes thinner and weak.

For the above described reasons, a sufficient strength of the outerperipheral side 6a of the peripheral portion 6 enough to withstand thepressure caused in a curling process was not attained.

SUMMARY OF THE INVENTION

In brief, conventionally it was simply believed that by folding aperipheral portion to be U letter shaped in section the strength of ananode container element or a lid of a battery container is increased andaccordingly leakage of an electrolyte is prevented. However, inactuality it has been observed that there is much room left forimprovement both in the strength to withstand curling and in preventionof leakage of an electrolyte.

The present invention is aimed to eliminate such problems as leftunsolved. Briefly described, the present invention relates to a changein a sectional structure of a lid of a battery container. Morespecifically, a sectional configuration of a lid of a battery containeris changed so that a lid having a predetermined volume of material maybring about the best advantage both in strength to withstand curling andprevent leakage of an electrolyte, inasmuch as the volume in material ofthe lid most effectively contributes to improvement in the strength andimprovement in prevention of leakage of an electrolyte.

More specifically, according to the present invention, a lid of abattery container element is formed with a peripheral portion U lettershaped in section, wherein the outer peripheral side of the peripheralportion U letter shaped in section is made thicker than the innerperipheral side of the peripheral portion U letter shaped in section. Inorder to manufacture a lid of such shape in section, a blank cut to thesize of a lid to be attained is prepared and the periphery of the blankis bent in one direction vertical to the surface of the blank and thenthe blank is subjected to pressure so that the edge of the bent portioncomes to be close to the central portion of a main flat portion of theblank in terms of the direction vertical to the surface of the blank,whereby the periphery of the blank is formed to be U letter shaped insection. By the above described pressing step the thickness of the outerperipheral side of the peripheral portion U letter shaped in section isfavorably increased as compared with the thickness of the innerperipheral side.

In a preferred embodiment of the present invention, the step of formingthe sectionally U letter shaped portion comprises the step of plasticdeformation for biasing the material of the inner peripheral side at thelower end of the peripheral portion U letter shaped in section towardthe outer peripheral side. As a result, a portion of an increasedthickness is formed in the outer peripheral side and at the same timeworking hardening contributing to enhancement of the strength is alsobrought about.

In another preferred embodiment of the present invention, the step offorming the peripheral portion U letter shaped in section comprises thestep of plastic deformation for forming an oblique surface outward atthe upper end of the outer peripheral side of the peripheral portion Uletter shaped in section. As a result, a lid that can be advantageouslyutilized in a very thin battery container is provided.

Accordingly, a principal object of the present invention is to provide alid of a battery container having a structure which is capable of fullywithstanding a curling force and preventing leakage of an electrolyte,and a method of manufacturing the same.

These objects and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view, partially in section, showing a conventionalsilver oxide battery for explaining the prior art of interest to thepresent invention;

FIGS. 2 to 8 are end views of mid-sectioned part showing in successionthe different steps of manufacturing the lid of the FIG. 1 battery;

FIG. 9 is an enlarged view of the peripheral portion of the lid;

FIGS. 10 to 12 are end views of mid-sectioned part showing in successionthe steps of the inventive method;

FIG. 13 is an enlarged view of the FIG. 12 step;

FIG. 14 is a view showing a test method employed to confirm the effectof the present invention; and

FIG. 15 is a front view, partially in section, showing a silver oxidebattery completed using an anode container element achieved inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 10 to 12 are end views of mid-sectioned part showing in successionthe steps in accordance with one embodiment of the inventive method.FIG. 13 is an enlarged view showing the FIG. 12 step.

Referring to FIG. 10, a blank 21 is prepared which is cut to the sizefor an anode container element serving as a lid of a battery containerto be obtained. The size of the blank 21 is determined taking intoconsideration a margin being bent in a bending process to be describedsubsequently.

Referring to FIG. 11, the blank 21 is subjected to a bending process atthe outer peripheral portion by means of a punch 22 and a die 23. Sincea portion being bent 24 of the blank 21 existing between the punch 22and the die 23 has a sufficient clearance, the thickness of the blank 21is not decreased at the peripheral portion, as compared with a drawingprocess conventionally employed. The outer diameter of the portion 24being bent is defined by the inner diameter of the die 23 and the innerdiameter of the die is selected to be equal to the outer diameter of ananode container element to be obtained.

Referring to FIGS. 12 and 13, the blank 21 which is a material beingfurther worked or processed is pressed between a punch 27 and a knockout28, while the same is confined by a die 26, whereby the material beingworked is forcedly formed to a desired shape. More specifically, thepunch 27 is formed with an acting portion 29 for pressing the edge ofthe portion being bent 24. The knockout 28 is formed with an actingportion 31 for pressing the central portion of the main flat area of theblank 21, with an oblique surface 32 formed outward and upward on theouter peripheral surface of the acting portion 31.

When the blank 21 is pressed by the above described punch 27 and theknockout 28, the blank is formed into a shape wherein the centralportion of the main flat area of the blank 21 is relatively swelledupward, while the portion being bent becomes thicker or increases thethickness. More specifically, the material of the inner peripheral side33b at the lower end of the peripheral portion 33 U letter shaped insection partially constituted by the portion being bent 24 is moved orbiased toward the outer peripheral side 33a as a function of the obliquesurface 32. As a result, a thickness for sufficiently withstanding theforce exerted in the direction A which becomes the maximum stress on theoccasion of a curling process is achieved. Furthermore, such thicknesscan also fully withstand the force exerted in the direction B beingapplied in a secondary manner on the occasion of the curling process.

Furthermore, it is further to be noted that hardening is caused due toworking of the material at the outer peripheral side 32a in particularof the peripheral portion 33 U letter shaped in section due to pressurebetween the above described punch 27 and the knockout 28. It is to befurther noted that the portion of the inner peripheral side 33b asshaped along the oblique surface 32 of the knockout 28 comes to performa function of a rib with the excessive material thereat. It has beenobserved that the above described hardening through the working processand the above described rib effect advantageously act on a curlingprocess. In addition, the above described hardening through working andthe above described rib effect also advantageously act on prevention ofleakage of an electrolyte and adhesiveness of the packing 7.

FIG. 14 shows a manner of testing the effect of the present invention.Referring to FIG. 14, both the anode container element obtained inaccordance with the conventional method and the anode container elementobtained in accordance with the inventive method are placed in thevertical direction with the same supported by a jig 34. Then the same ispressed from upward by a presser 35 and the maximum compression load onthe occasion of the primary buckling was measured. An average value wasevaluated by five values measured on five samples on each of theconventional ones and the inventive ones and as a result the averagevalue for the conventional ones was 16.60 kg whereas the average valueof the inventive ones was 17.25 kg. Thus it was substantiated that thepresent invention is superior to the conventional one.

Furthermore, the hardness of the respective portions of the conventionalones and the inventive ones was measured and the following result wasobtained. More specifically, the Vickers' hardness was measured withrespect to each of the portions a to e in FIGS. 9 and 13 using aVickers' hardness tester under the measurement condition of 15 sec. witha load of 200 g. As a result,

at the point a, the conventional one was 208, whereas the inventive onewas 205,

at the point b, the conventional one was 296, whereas the inventive onewas 253,

at the point c, the conventional one was 306, whereas the inventive onewas 381,

at the point d, the conventional one was 369, whereas the inventive onewas 446, and

at the point e, the conventional one was 369, whereas the inventive onewas 420.

Thus it was confirmed that hardening through working has occurredparticularly at the peripheral portion 33 U letter shaped in section.

FIG. 15 is a front view, partially in section, showing a silver oxidebattery implemented using an anode container element fabricated inaccordance with the present invention. The anode container elementpracticing the present invention is denoted by the reference numeral 40.The other elements are the same as those shown in FIG. 1 and hence thesame portions have been denoted by the same reference numerals and adescription thereof is omitted.

Referring to FIG. 15, the anode container element 40 comprises theperipheral portion 33 U letter shaped in section attained in accordancewith the above described process. The anode container element 40 and thecathode container element 1 are mechanically coupled through mutualengagement of the peripheral portion 33 of the anode container element40 and the opening edge of the cathode container element 1. Morespecifically, the packing 7 is disposed outside the peripheral portion 6and the opening edge of the cathode container element 1 is curledinward. As a result, a tight seal structure for preventing leakage of anelectrolyte is achieved.

Meanwhile, referring to FIGS. 12 and 13, an outer surface extendingstraight in the upward and downward direction was formed on the outerperipheral side 33a of the peripheral portion 33 U letter shaped insection. In addition, the above described outer surface has beenprolonged in the upward and downward direction on the straight extendingsurface, as compared with a case where the conventional outer peripheralside 6a is formed to extend from the bent portion 6c as naturally bent.The above described straight outer surface extending in the upward anddownward direction plays an important role in ensuring a tight seal withthe packing 7 on the occasion of curling in the direction A performed inthe curling operation of the cathode container element 1. In thiscontext, the longer the straight outer surface the better in preventingleakage of an electrolyte. According to the present invention, itbecomes more easy to form longer the outer surface extending straight inthe upward and downward direction.

According to another embodiment of the present invention, a particularlythin or low battery container can be advantageously provided as shown bya phantom line in FIG. 13. More specifically, the acting portion 29 ofthe punch 27 is further formed with an oblique surface 30 which isinwardly and downwardly oblique. This oblique surface makes it possibleto form an outwardly oblique surface at the upper end of the outerperipheral side 33a of the peripheral portion 33.

According to the cathode container element 5 formed with an obliquesurface faced outward at the upper end of the outer peripheral side 33a,the opening end portion of the cathode container element 1 is receivedby the above described oblique surface when the opening end of thecathode container element 1 is curled inward and therefore a fataldisadvantage of the conventional approach that the opening edge of thecathode container element 1 further protrudes from the outer mainsurface of the cathode container element 5 is advantageously eliminated.

As described in the foregoing, according to the inventive lid of abattery container, the outer peripheral side of the peripheral portion Uletter shaped in section can be formed in an increased thickness andtherefore a sufficient strength to withstand the load on the occasion ofcurling is provided and accordingly a curling operation can be made witha sufficient strength, thereby to enable an assured tight sealstructure, with the result that leakage of an electrolyte is effectivelyprevented.

According to the inventive method, a blank of a predetermined size isfirst bent in one direction vertical to the surface of the blank at theperiphery thereof and then the blank is subjected to depression so thatthe edge of the portion being bent comes to be close to the centralportion of the main flat portion of the blank in terms of the directionvertical to the blank, whereby the peripheral portion is U letter shapedin section and therefore the outer peripheral side of the peripheralportion U letter shaped in section in particular can be readily madethick. Furthermore, in the process of forming the peripheral portion ina U letter shape in section, this portion is advantageously subjected tohardening due to working.

It is to be pointed out that the present invention is not limited tofabrication of a battery container for a silver oxide battery but thepresent invention can be equally applied to a battery container of anyother types of batteries, such as a silver peroxide battery, a mercurybattery, a lythium battery, a closed type nickel-cadmium battery, aalkaline-manganese dry batter and the like.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A method of manufacturing a lid of a batterycontainer having a peripheral portion U letter shaped in section forengagement with a main body having an opening edge of said batterycontainer through a packing with said opening edge of said main body ofsaid container curled inward, comprising the steps of:preparing a blankcut to the size of a lid being obtained; bending the periphery of saidblank in one direction vertical to the surface of said blank to producea U-shaped periphery; and pressing the edge of the bent portion of saidblank and the central portion of the main flat portion of said blank inthe directions toward each other in terms of the direction vertical tothe surface of said blank to plastically deform the lower edge of saidperipheral portion so that the material at the inner peripheral side atthe lower end of said U-shaped periphery is biased toward the outerperipheral edge so as to form on said lower end a horizontal surfacefacing downward, an oblique surface extending from the inner peripheraledge of said horizontal surface and facing downward and inward, and avertical surface extending from the outer peripheral edge of saidhorizontal surface and facing outward.